Production of pulp, etc



Patented May 31, 1932 I UNITED STATES.

PATENT o'l-"F 1'c1-: j;

LINN BRADLEY, or MONTCLAIR, NEW JERSEY, AND EDWARD r. IlIcKEEIE,or'rria'r'rst BURG, NEW YORK, ASSIGNORS T0 BRADLEY-McKEEFE oomgonarromorNEW YORK,

N. Y., A CORPORATION or NEW YORK.

raomrc'rron or PULP, ETC.

No Drawing. Application filed July 3,

This invention relates to the production of chemical pulp from wood andto the regeneration of the cooking liquors. h

More particularly it relates to the cooking of wood chips withcookingliquors which,

contain sodium sulfide and sodium sulfite as the primary or the soleactive reagents, and to the treatment of the residual liquors therefromand the regeneration of cooking liquors for use in the same type ofcooking process. Moderate amounts of other chemicals may be present inthe cooking liquors, e. g. sodium hydroxide, sodium carbonate, sodiumthiosulphate, sodium sulphate.

Among the objects of the invention'is the containing a substantialaniount of sodium" sulfite; the residual liquor, referred to herein asblack liquor, is separated from the pulp, the pulp is Washed and thewashings (a suitable amount) is added to the blackliquor (the mixturebeing referred to as weak black liquor): the Weak black liquor isconcentrated, the organic matter is decomposed by heat treatment, thesodium compounds being obtained principally in the form of sodiumsulfide and sodium carbonate. A solution of suitable strength isprepared from Y the recovered sodium carbonate and sodiumsulfide, and acooking liquor is prepared p therefrom which is thereafter utilized inthe digesting step. a y 1 f In the preferred embodiment of the inven-1"92e. Serial No. 120,514.

tion', the cooking liquor is either substantialum hydroxidei's present.in limited amount, e. g, less than the amount of sodium sulfide. Forexamplesqthe: cooking liquor may contain 50 parts as Na s, 25 parts asNaOI-I, 25

parts as Na SO all being computed on an 1y free from sodium hydroxide,or the sodi- Na O basis; that is to say, about 50 parts Na S, about25.64 parts NaOH, and about 40.39 parts Na sO 4 '50 parts as Na s, 40parts as Na SO 10 parts as NaOH; that is to say, about parts of Na S,64.62 parts Na SO 10.26 parts NaOH. I

5O parts as Na s, 45 parts as Na SO 5 parts as NaOH; that is to say,about 50 parts of Na S, 72.7 parts of Na SO 5.13 partsof NaOH.

Various other, ratios of these active compounds may be contained in. thecooking liquors of this process, and other chemicalsmay a The amount ofthe be present in moderate amounts, e. g. Na CO Nagsgoa Nagsoh etcactivereagents used, in proportion to the wood digestedv by such cookingliquors may vary somewhat, but sufiicient sodium Isulphideis employed toperform a very substantial portion, of the digestion, which mayihesupplementedby the NaOH and the Na SO or by the Na SO alone when no'NaOHis present. 1 1 e In computing the activity of the cooking liquor, allof the NaOH and of the Na S' is considered as available, and from /4 toof the N32801:, is likewise considered. Some of" the Na SO appears to beconverted into Na S O in the digestion step as a result of" the reactionbetween Nags andw'ood substance. An activity of. about (Na s equivalent)is generally sufficient for I most woods,'.the higher amounts beingem-3'1? cals dto yield the desired .product'from the 'woo The digestionor cooking step is carried loyed for wood which requires more chemi-.out in a manner similar to that employed in which escapes with thevapors when the di-- gester is relieved and when the digester contentsare blown at the end of the cook. This appears to modify the odors in anadvantageous manner, and is further desirable owing to the retention ofthe sulphur in :the residual liquor.

When the residual liquor is concentrated and the organic matter isdecomposed by heat treatment in the presence of a current of hot gases,some sulphur is eliminated along with the gases. In order'to retain aconsiderable amount of sulphur in the product, the

' furnacing operation is so carried outFas to facilitate the productionof sodium sulfide in the recovered soda product. For example, the stackgases are' scrubbed by the black liquor soas to absorb some of thesoluble sulphur cpmpounds and to regain some of the soda carried by thegases. Air is introduced at any suitable point, e. g. between thecalcining furnace and the scrubber so as to oxidize some sulphurcompounds, e. g. 'H S, COS, etc. if present, so as, to facilitate their-recovery by the scrubbing operation and thus promote the production ofa recovered product containing a high percentage of Na S. The-hotfurnace gases ap ear to eliminate some of the sulphur as (18S byinteraction betweenCO and 'S. When the COS is burned some S0 or S0 isformed which is more easily absorbed in the black liquor used in thescrubber. The furnace operation is so conducted as to obtained a highpercentage of Na S and care is taken not to prolong the furnaceoperation;-

'45 -phide and other soluble sodiumcompounds The. sodium cai'hbnatej'andsodium sulin the recovered furnace product are disso1ved,in-water orweak cooking liquor, for

example, andlthe solution is clarified by any suitable means beforebeing employedin the cookingoperation. 1

Sodium sulphate ma" be employed for replacing soda losseswhich'are,however, kept low owing to, the scrubbing of the stack gases. Sodiumsulphate may be added at any suitable point, e. g. to the material en-;

' tering the furnace in which the reduction treatment occurs by which NaS is formed.

In case some NaOH is desired in the cook ing liquor. asuitable amount ofCa(OH) be added to the, Na CO Na s liquor 'to convert thedesircd'portionof Na CO- into NaOH. I The CaCO mud formed aids in the" clarification ofthe liquor. By keepingthe amount of NaOHthus produced and ,the

amount of lime mud thus formed, down to a the washing of such lime mudis dispense with, which is a distinct advantage.

In case Na SO isdesired in the cooking liquor, in greater amount thanalready present in the NmS-NznCO liquor, a further amount of Na SOg maybe formed therein by .treating the solution with the required amount ofCaSO The mixture is agltated for sufficient time to convert the CaSO forthe most part or substantially completely, in'toCaCO and formacorrespondingamount of Na SO in the solution by reaction with Na COthereof. .The liquor .is' separated from the CaCO mud, the latter iswashed to remove the soda compounds to a considerable extent. thusfreeing the CaCO mud from most, of the sulphide associated therewith inthe solution. After such washing, the CaCO mud may then be moreadvantageously treated with an acid sulphite solution, e. g. a solutionprepared by dissolving Sf) in water. This treatment is so regulated thatsubstantially all of the, CaCO is converted into CaSO The mixture of theacid solution and theCaCO is suitably a- 'itated to promote thereaction, and when su 'stantially all of the CaCO has been thus converted, and that solution has been nearly or substantially neutralizedby removal of uncombined S0 the mud is separated from the liquor. Thismud may be used for convertmg more -Na3CO3 into Na $O in the mannerabove outlined.

The liquor may be used for' absorbing more S0 to'prepare anotherchargeof acid sulphite solution to be employed for treating anotherbatch of CaCO mud. It is advantageous to thus reuse the liquor owing tothe retention of the soda compounds which may be present therein, e. g.when the (la-C05 mud has not been fully washed to remove the sodacompounds. Too much NaS should not be permittedto remain in the CaCO mudsince this is readily converted into-some Na S O .when

treated with the acid sulphite solution. A sinall amount of Na s may bethus tolerated andsimpli-fication of/the washing problem effected.

solution, and the amount of liquor carried along by the CaS O mud," 1naybe regulated so as to introduce the desired portion of soda as Na- SOBy using a dilute circulating sulphite solution, and removing most ofthe solution from the CaSO mud, the amount of 5 soda thus removed may bekept very low, and

still have it present in the solution.

When the CaSO mud or the 03002 mud becomes fouled, from any cause, thewhole or any required portion thereof may be discarded, preferably ;asCaCO mud. This should be Well washed before'it is dischar ed, to regainthe soda. If desired the Cal mud, or aportion thereof, which is to bediscarded, may be employed, prior to its being discarded, for thetreatment of the NaCO Na s liquor to clarify it. The mud and sedi- 'ment,, e. g. carbon, etc., may be washed and the washings retained and thewashed mild discardedw The make-up of lime compounds may be supplied inany suitable manner, e. g. it may be advantageously supplied by adding(3210, or Ca(OH) in therequired amount to replace losses, to the liquorwhich contains the Na CO -Na S to form a corresponding amount of NaOHtherein. The Ca(OI-I) may even be mixed with the CaSO mud and p the twoemployed together or the make-up lime may be added in part to the Na CONa s li uor to clarify it and another portion of Ca( H) to the CaCO orthe CaSO whichv is first sulphited and then used to produce Na SO and isreturned to be again sulphited. By first clarifying 35. the liquor, andfreeing it from any. objectionable. compounds, e. g. iron compounds, andavoiding objectionable compounds in the CaCO mud or the CasO 'mud, thesem'uds may be utilized .over and over again for several times, thusminimizing the problem of discarding a portion thereof in order toremove accumulated objectionable material.

The amountof sulphur burned to form S0 means described, can beregulated. Ordinarily the amount will be regulated so that the desiredNa s content may be obtained in the cooking liquor. Where the sulphurretention is very high, e. g; owin to good scrubber recovery, the amountof S6 sulphur thus supplied can be kept very low, and especially whereNa' bo is added for make-up.

The amount' of S0 added to the cycle should be enough to insure theproduction of the. required amount of Na s in the cooking liquor, andwhere the amount of NaOH in the cooking liquor is very low, such a highsulphide is desirable as will carry out most 99 of-the cookingoperation, being su lemented by the moderate amount of Na s l present.When the cooking .li uor is free from or very low in NaOH, the I\a SOproduced should be somewhat more than sufficient to convertpolysulphides, if present, into normal suland. then, indirectly form NaSQB by the phide and into some Na S o Care should be taken, however, inthe furnacing operations, to keep the polysulphides down to a very lowpoint, and preferably absent from. the Na S-Na CO liquor. By having aconsider able amount of Na SO in the cooking liquor, a high Na s contentmay be safel employed and obtain high quality pulp. he Na sO appears toovercome several objections to the use of a high Na S alone. a

By this process, a large number of woods may be readily converted intochemical pulp of high quality and high yield. The process is cyclic incharacter, and the soda content can be repeatedly used in the manneroutlined.

' The present case is a continuation in art of our co-pendingapplications Serial os. 57,953 and 57,954, filed September 22, 1925.

We claim:

1. The method of producing wood pulp from wood which comprises cookingthe wood in a cooking liquor comprising as its threeessential chemicalreagents sodium hydroxide, sodium sulfid and sodium sulfite, the sodiumoxide equivalent of the sulfid being greater in amount than the Na Ocontent of either the sodium hydroxide or the sodium sulfite, and theamount of sodium present as sodium. sulfite being at least one half butless than the amount of sodium present as sodiumsulfidv 2. The processwhich comprises cooking raw cellulosic material in an alkaline cookingliquor containin as essential chemical reagents sodium sul d and sodiumsulfite, separating the pulp from the spent cooking liquor,concentrating the spent liquor and calcining the dried product underreducing conditions to produce a furnace'product containing sodiumsulfid and sodium carbonate with evolution of sulfur-bearing gases fromthe furnace during the furnacing operation, oxidizing the gases from thefurnacing operation with air and passing the oxidized gases in'contactwith spent cooking liquor for the recovery of oxidized sulfur compoundsfrom the gases in the spent'liquor, removing water from the resultingspent liquor, furnacing the resulting dried product under reducingconditions to form sodium carbonate and sodium sulfid, preparing asolution containing such sodium carbonate and sodium sulfid, sulfitingsodium carbonate thereof to prepare cooking liquor containing the sodiumsulfid and sodium sulfite, and cooking rawcellulosic material with theprepared cooking liquor. 3. The further improvement in claim 2. in whichthe alkaline cookin liquor contains sodium present as sodium sulfite inan amount not less than one half but less than that present in thesodium sulfid. .e- 0

4. The further improvement in claim 2, in which the alkaline cookmgliquor contains 130 I essential chemical reagents sodium sulfid andsodium sulfite, the amount ofsodium present therein as sodium sulfitebeing not less than one half but less than the amount of sodium presenttherein as sodium sulfid and said liquor being free from sodiumhydroxide in amounts arger than one half the amount of sodium sulfidtherein.

wood, which comprises digesting the wood in an alkaline cooking liquorcontalmng as its three essential chemical reagents sodlum' sulfid,sodium sulfite and sodium hydroxide, the liquor containing for ;each 50parts of sodium sulfid at least. parts but not more than 45 parts ofsodiumsulfite and at least 5 parts but not more than 25 parts of sodiumlgydroxide, all being computed on an Na O asis. 1 y

r 7 The process which comprises the following steps :(a) digesting rawcellulosic fibrebearing material in an alkaline cooking liquorcontaining sodium sulfid and sodium su fite; (-b) separating theresulting alkaline liquor from the resulting fibre-bearing material; (a)removing water from the resulting alkaline liquor; (d) furnacing driedconstituents thereof under reducing conditions to form sodium carbonateand sodium sulfid; (e) dissolving these latter sodium compounds inwater, thereby forming an alkaline solution; (f) treating the alkalinesolution with material including a normal sulfite of an alkaline earthmetal to convert sodium carbonate thereof into sodium sulfite, therebyproducing an alkaline cooking liquor which contains sodium sulfid andsodium sulfite; (g) separating the alkaline cooking liquor from theresulting alkaline earth metal carbonate; (h) digesting raw cellulosicfibrebearing material with the alkaline cooking liquor; (2') convertingthe alkaline earth metal carbonate into an alkaline earth metal sulfiteby means of available S0 and using such metal-sulfite to treat analkaline solution which contains sodium carbonate and sodium sulfidobtained as a result of the furnacing of dried constituents as per step(d). -8-. The cyclic process which comprises the following steps :(a)digesting raw cellulosic fibre-bearing material in a cooking liquorcontaining a sulfite of sodium; (6) separating the resulting liquor fromthe resulting fibre-bearing material; (0) removing wasulfid; (e)dissolving these latter sodium com- 6. The method of producing pulp fromcarbonate, thereby'eflt'ecting a clarification of ter from the resultingliquor; (d) furnacing dried constituents thereof underreducingconditions to form sodium carbonate and sodium pounds in water,thereby forming an alkaline solution; (f) treating the alkaline solutionwith material including calcium hydroxide to convert a portion only ofthe sodium carbon ate thereof into sodium hydroxide; (g) separating thepartly causticized solution from the resulting calcium carbonate,thereby effecting a clarification of the solution; (h) 'sulfiting theclarified liquor to convert sov dium carbonate thereof into sodiumsulfite;

(1i) and digesting raw cellulosic-fibre-bearing Material withcookingliquor containing the resulting sodium compounds.

9. The cyclic process which comprises the following steps :(a) digestingraw cellulosic fibre-bearing material in a cooking liquor containingsodium sulfid and sodium sulfite; (b) separating the resulting liquorfrom the resulting fibre-bearing material; (0) removing water from theresulting liquor; (d) furnacing dried constituents thereof underreducing conditions to form sodium carbonate and sodium sulfid; (e)dissolving these latter sodium compounds in water, thereby forming analkaline solution; (f), treating the alkaline solution with materialincluding calcium hydroxide .to convert a portion only of the sodiumcarbonate thereof into sodium hydroxide; (g) separating the partlycausticized solution from the resulting calcium the solution; (h)treating the clarified solu tion with a sulfite of an alkaline earthmetal to convert sodium carbonate thereof into sodium sulfite andproduce an alkaline cooking liquor, containing sodium sulfid and sodiumsulfite; (i) separating the alkaline cooking liquor from the resultingcarbonate of the alkaline earth metal; (7') and digesting raw cellulosicfibre-bearing material in such alkaline cooking li uor'.

10. The furt er improvement in the process of claim 9, characterized bysulfiting the carbonate of alkaline-earth metal with available S0 afterit has'been separated from the alkaline cooking liquor in step (2')thereof, and subsequently using the resulting sulfite of alkaline earthmetal in step (h) thereof.

11; In a cyclic process for producing pulp from woodin which wood isdigested by means of cooking liquor that contains at least as much ofsodium sulfid as of sodium hydroxide and in which the residual liquorcycle in the form of the sulfite radical in such an amount that thecooking liquor contains at least one half as much but not more sodium assodium sulfite as it contains as sodium sul- 5 fid, thereby providingthe cooking liquor with sodium sulfite in amount sufiicient to modifyobjectionable odors of the conventional sulfate process and providingthe residual liquor with oxy-sulfur material sui'ficient to insurethepresence of sodium sulfid in the regenerated cooking liquor.

In testimony whereofwe aflix our signatures.

LINN BRADLEY. EDWARD P. McKEEFE.

